There has been conventionally a friction stir spot joining device for softening and stirring an object to be joined by frictional heat generated by rotation of a pin so as to perform spot joining, and provided with a stirring motor for rotating the pin and a pressure application motor for driving the pin to be moved straight (for example, see Patent Document 1).
There has been also a friction stir spot joining device for softening and stirring an object to be joined by frictional heat generated by rotation of a center pin and a shoulder pin so as to perform spot joining, and provided with a stirring motor for rotating the shoulder pin in which the center pin is inserted, a motor for driving the center pin for causing the center pin alone to be retracted, and a pressure application motor, wherein a shaft of the shoulder pin and the stirring motor are connected to each other by a power transmission mechanism, and a shaft of the center pin and the motor for driving the center pin are connected to each other by another power transmission mechanism so as to integrate stirring-related members, and bearings of a linear motion guide are fixed to a lower portion of the power transmission mechanism for the center pin behind thereof, a ball nut is fixed to the back face of the integrated stirring-related members, and the pressure application motor is fixed to a friction stir spot joining device body to which rails of the linear motion guide are fixed and which contains therein the integrated stirring-related members, and wherein the screw shaft connected to the pressure application motor is caused to screw with the ball nut so as to advance or retract the integrated stirring-related members (for example, see Patent Document 2).
Patent Document 1 JP 2002-35960A
Patent Document 2 JP 2007-216249A
According to the friction stir spot joining device described in Patent Document 1, since the stirring motor for rotating the pin is fixed to the friction stir spot joining device body side like the pressure application motor, when the pin is driven so as to be moved straight, there occurs a phase difference in a positional relation between the stirring motor and the pin, so that a spline mechanism is adopted for transmitting the rotary motion of the stirring motor to the pin. Owing to the spline mechanism, a straight moving stroke of the pin is restricted by the length of a groove of the spline and there is a possibility that the entire friction stir spot joining device is large sized.
According to the friction stir spot joining device described in Patent Document 2, since it adopts a configuration wherein the stirring-related members are integrated, and the pin and the stirring motor are moved at the same time inside the friction stir spot joining device body relative to the pressure application motor fixed to the friction stir spot joining device body side, the problem of Patent Document 1 is tentatively solved by the configuration of the friction stir spot joining device disclosed in Patent Document 2. However, since the integrated stirring-related members are entirely contained in the friction stir spot joining device body, when performing maintenance or assembly of the stirring-related members, the stirring-related members are difficult to take out and assemble, and the stirring motor and the power transmission mechanism for the stirring motor cannot be solely removed or replaced. Further, since the bearings of the linear motion guide are fixed to the lower portion of the power transmission mechanism behind thereof, a large burden is applied to the bearings of the linear motion guide, causing a problem that the pin side is liable to vibrate and so forth.